Hybrid and electric vehicles (HEVs) typically include an electric traction drive system that includes an alternating current (AC) electric motor which is driven by a power converter with a direct current (DC) power source, such as a storage battery. Motor windings of the AC electric motor can be coupled to inverter sub-modules of a power inverter module (PIM). Each inverter sub-module includes a pair of switches that switch in a complementary manner to perform a rapid switching function to convert the DC power to AC power. This AC power drives the AC electric motor, which in turn drives a shaft of HEV's drivetrain. Traditional HEVs implement two three-phase pulse width modulated (PWM) inverter modules and two three-phase AC machines (e.g., AC motors) each being driven by a corresponding one of the three-phase PWM inverter modules that it is coupled to.
Many modern high performance AC motor drives use the principle of field oriented control (FOC) or “vector” control to control operation of the AC electric motor. In particular, vector control is often used in variable frequency drives to control currents fed to a three-phase AC electric motor so that angular velocity of motor's rotor can be controlled and hence the torque applied to a shaft can be controlled. In vector control, stator phase currents are measured and converted into a corresponding complex space vector. This current vector is then transformed to a coordinate system rotating with the rotor of the three-phase AC electric motor. This technique requires knowledge of the rotor's angular position (i.e., the mechanical rotational angular position of rotor relative to the “stator” or motor windings).
The rotor's angular position can be computed based on actual measured quantities using some type of speed or position sensor for control feedback measurement. For instance, to determine the angular position of the rotor, its angular velocity can be measured with a speed sensor, and the angular position can then be obtained by integrating the angular velocity measurements.
Other field-oriented or vector controlled systems may use a rotor angular position sensor or rotational transducer that provides absolute position information directly to implement motor control techniques. One such example would be a resolver and resolver-to-digital converter circuit, which directly provides position information that corresponds to the rotor's angular position.
The position sensor is an important device in providing necessary information regarding the rotor's angular position. However, in some cases a position sensor can experience a fault or fail in which case position measurements provided by the position sensor will usually be incorrect or missing completely. For instance, a loss-of-tracking (LOT) failure can result, for example, when the motor is operating in its overspeed region and the rotor's angular velocity (or “motor speed”) exceeds a tracking threshold limit of the position sensor. Alternatively, LOT failure can also result, for example, when an internal position error of the position sensor exceeds a certain preset threshold. When a position sensor experiences a LOT failure, the rotor angular position measurements that are normally provided by the position sensor will usually be incorrect or missing completely. As such, it becomes necessary to immediately shutdown the electric motor-drive since it relies on this information to ensure correct operation.
Once the rotor's angular velocity returns to within the position sensor's tracking limits, many electric motor-drive systems enter a position sensor recovery mode (PSRM). Before placing the motor control processor back into its normal field-oriented or vector control operating mode, it is prudent to verify the accuracy of the position sensor's angular position output to ensure that the position sensor is generating valid angular position information. Otherwise, it is likely that field-oriented vector control techniques will not work as intended since the rotor angular position information they rely upon from the position sensor could be inaccurate.
It would be desirable to provide improved methods, systems and apparatus for verifying the accuracy or inaccuracy of a position sensor's angular position and velocity outputs following a position sensor fault/failure. It would also be desirable if such improved methods, systems and apparatus simultaneously allowed for a rotor's angular position and velocity (or “motor speed”) to be estimated while the position sensor is in fault or failure mode. It would also be desirable if such improved methods, systems and apparatus worked with AC motors including permanent magnet synchronous motors (PMSMs). Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.